The performance was Cooper's first at the prestigious awards show. The actor sang "Shallow" from A Star is Born with Gaga, and fans couldn't get enough. The pair graced the stage unannounced, stepping out of the audience together. Many fans had been looking forward to the duet long before the big night. Most were, once again, taken aback by the chemistry between the two stars.

They kicked off the performance sitting across from one another, singing their respective parts. Toward the end, Cooper joined Gaga behind the piano. The pair shared a mic, as well as an intimate moment. It appeared, at one point they might even lock lips.

Rumors have been swirling about Cooper and Gaga for some time, largely because of their palpable chemistry. Cooper is, of course, with partner Irina Shayk, who he started dating in 2015 and who attended the 2019 Oscars with him. Gaga, however, is newly single after ending her engagement.

"The way Lady Gaga and Bradley Cooper look at each other --- I don't feel safe," said one fan on Twitter.

Another tweeted, "Finally. Bradley Cooper and Lady Gaga give the Oscars the life support it needs. And Gaga's necklace needs an Oscar on its own."

"I just got my ENTIRE life from that @ladygaga and Bradley Cooper performance #Shallow #Oscars," joked a third Twitter user.

See more reactions to Lady Gaga and Bradley Cooper's "Shallow" performance at the 2019 Academy Awards, below.

Cooper was equally excited about taking the stage. Ahead of the show, he told People he was in disbelief that he'd be performing live with Gaga. He added, however, that he was excited.

"That's so surreal that I said yes we will be performing tonight," he said. "I'm very excited."

It's not the first time he's done it, though. Cooper came out during one of Gaga's Las Vegas residency shows in January to surprise concertgoers. The pair shared a hug before diving into the hit song.

A Star is Born, directed by Cooper, is nominated for seven awards. It's up for Best Picture, Best Actor, Best Actress, Best Supporting Actor, Best Adapted Screenplay, Best Cinematography, and Best Sound Mixing.

Editor's note: An earlier version of this article erroneously referred to Irina Shayk as Bradley Cooper's wife. We regret the error.